A cohort study is planned to determined the incidence of new primary cancers in patients with Hodgkin's disease. The patients will be identified through the cancer registry at the Memorial Sloan-Kettering Cancer Center. Cohorts receiving treatment for the first time during 1950-54, 1960-64, 1965-69 and 1970-74 (approximately 1500 patients) will be followed until death or the termination date of the study, December 31, 1979. The study will attempt to determine whether the incidence of metachronous primary cancers varies with the extent of disease and/or histopathologic classification prior to first treatment of Hodgkin's disease. A major objective will be to determine to what degree radiotherapy and chemotherapy acts as oncogenic agents after sufficient latency and intensity of exposure. The cumulative exposure to ionizing radiation will be estimated in relation to number of treatments, fractionation, energy source and volume of tissue irradiated.